Finish Floor Elevation

How did you get the information about the benchmark? What is the source of this data, the 3.5'?

Call a surveyor, request an elevation certificate (I think that's how they call it), that should answer your question and provide you peace of mind.

Understood, that is what they are doing. I just want to know how it is figured.

Not exactly sure what your asking. Does the finished floor need to be at an elevation of 7.0', and the manhole is 3.5'?

No it's not added. If the BM is 3.5 and the FF is to be at 7.0 you go to 7.0. So you need to be 3.5 above the BM. I assume you're saying the finished floor elevation needed is 7 foot. If so then whatever the value of the benchmark is subtract that from 7 to get the value you have to go up.

However the value not being out to the thousands I doubt it's a certified benchmark.

Follow to that: I'm assume those are just number to get your point across? Nowhere in fla is the ground elevation 3.5 and the FF REQUIRED only 7.0. Sounds like your close to the coast at 3.5 on a manhole. Should be 17-20 feet for FF

Yes, the elevation has to be at 7.0'. The benchmark is 3.50'So if I undersatnd correctly, just subtract 7.0 -3.50. FFE is 7.0'

Correct. 7.0-3.5=3.5.

Correct, the benchmark on the manhole is 3.50 (yes, close to the coast)FEMA requires 7.0 NAVD where I am located. Should be 17-20 feet for FF. How do you get 17-20, just curious. My neighbor down the street said is FFE is 10'.

Most coastal FEMA FF are higher than 7feet. Ground elevations that low are subject to storm serge. If you can go up 3.5 feet and not pay 10k in flood insurance and pass code than alls peachy. Never heard of it in 40 yrs on the west coast from tally to Naples.

I'm doing the right think and waiting for the survey. I was just interested how they figured the FFE. I looked at the plan closer, this is what it states:
Elevation of first habitable floor is +8'-0"NAVD
Applicable flood zone: AE 7.0' NAVD
Proposed Grade +5.8
Lot 24 (my lot) FEE 8.0 NAVD

Local jurisdictions vary. Around here FFE MUST BE BFE+2.

What does the permit say?

As an aside, manholes are horrible benchmarks. When the streets are milled or over layed the rings get re-used. Same mark different elevation. ..

> Follow to that: I'm assume those are just number to get your point across? Nowhere in fla is the ground elevation 3.5 and the FF REQUIRED only 7.0. Sounds like your close to the coast at 3.5 on a manhole. Should be 17-20 feet for FF

Why would you say that? He could easily be in a flood zone of those requirements with a road (manhole) elevation of only 3.5'

I live on the coast, in an AE 8 flood zone and the road in front of my house is very close to +4.

A FF requirement of 17-20 feet would likely (in my area of SW Florida) be directly on the Gulf of Mexico. And even then, not everywhere.

Heck, I can show you an X ZONE on the back bay on Captiva Island!

> As an aside, manholes are horrible benchmarks. When the streets are milled or over layed the rings get re-used. Same mark different elevation. ..

sure, but what are the odds of that happening during his construction?? And why assume it's the ONLY benchmark, anyway?

> I'm doing the right think and waiting for the survey. I was just interested how they figured the FFE. I looked at the plan closer, this is what it states:
> Elevation of first habitable floor is +8'-0"NAVD
> Applicable flood zone: AE 7.0' NAVD
> Proposed Grade +5.8
> Lot 24 (my lot) FEE 8.0 NAVD

Yes, it looks like the plan is for the slab to be One foot about BFE, which is always a good idea. Some counties add a "freeboard" requirement to the FEMA base flood.

so 8-3.5 would be the difference from the manhole to the proposed slab. I would hope your surveyor has (at least) two benchmarks on site to check between during construction.

Good luck!

Andy

'what are the odds of that happening during his construction??"

Too high to gamble on!!

In Florida, every topographic survey requires at least two benchmarks. And every surveyor should check between those two marks, especially when staking out a house.

I prefer to use storm drain catch basins with chiseled marks for BM's as they are stable and rarely modified. Even sanitary manholes aren't changed all that often.

If I was on his project, I think I would recognize if the suddenly overnight came in, cut out the rims and added risers and new asphalt to the road. But that's just me!

I mean, seriously, the guy posts a very simple survey related question and along with the answer, he is told that his floor MUST be wrong, his Benchmark is wrong and his surveyor probably has no idea what he is doing. Oh, and somehow the permitting agency forgot to add to the FEMA BFE.

Really guys, this is why we can't have nice things.

Andy

I didn't assume so. I simply pointed out something I have seen cost thousands. Some places have stable roads that are rarely modified, others not so much. At the end of the day my statement was what I called it. An aside meant to provoke thought...